1. Field of the Invention
This invention is directed to an improved system for the separation of contaminants, such as oil, from mixtures of such contaminants with water.
2. Prior Art
In recent years, an increasing awareness of the importance of maintaining the quality of the environment has led to the development of various methods for separating contaminants, such as oil, from aqueous effluents before discharging the effluents to the environment. A common application for oil-water separation processes is in the treatment of condensates from compressed air systems. Air compressors are typically lubricated with oil and, in operation, some of the lubricating oil becomes admixed with the aqueous condensate. Acceptable disposal of such oil-water mixtures and/or recycling of the components requires that they be separated. The simplest and most common approach to such a separation relies on the limited miscibility of oil and water and the differences in their specific gravities. Oil-water separators are known, utilizing a holding tank or settling chamber wherein the mixture is allowed to settle and the oil, being of lower specific gravity, rises to the surface, where it may be conveniently skimmed or drained off. The use of such a system may be reasonably effective for the removal of free oil. However, many oil-water mixtures contain additional oil in the form of oil-water emulsions. Separation of oil present in the form of an emulsion is more difficult and may require the additional use of a filter or oil-adsorbing medium, such as activated carbon or a clay type material.
Filtration is often carried out as a final "clean-up" step to remove residual traces of emulsified oil after gravity separation of free oil. A problem frequently encountered with the use of such filters for oil removal is that they often become filled, or clogged, with oil in the initial contact region. The oil tends to fill in the crevasses and pores to the point where water cannot readily penetrate the filter media beyond the first point of contact. The force of gravity fed water is often not sufficient to overcome the resistance of the oil collected at that point with the result that the filter media must be replaced long before its useful life fits complete.
U.S. Pat. No. 5,143,611 to Pate discloses a system wherein oil and water are separated by gravity, first in a primary separation chamber and then in a secondary separation chamber, positioned within the primary separation chamber. An additional separation is provided by an external activated carbon filter.
U.S. Pat. No. 5,196,117 to Billiett et al discloses the separation of an oil-water mixture by first passing the mixture through a coalescing filter to coalesce oil present as an oil-water emulsion in the mixture, to form free oil droplets. Free oil is then separated by passing the mixture to a settlement chamber wherein free oil rises to the surface and is removed therefrom. The remaining traces of oil are then removed by passage through a sorbent bed.
U.S. Pat. No. 5,196,123 to Guthy discloses a method and apparatus for the separation of oil from an aqueous condensate. The process utilizes a separation tank interconnected with an oil receiver tank to effect a gravity separation of the oil and water with a subsequent treatment of the separated water by passage through activated carbon for the further removal of residual trace amounts of oil.
U.S. Pat. No. 5,225,073 to Billiett et al. discloses an apparatus for separating a contaminant, such as oil, from water wherein an oil-water mixture is passed through a coalescing filter where some oil is separated and the remaining liquid is passed to a settlement chamber where additional separation takes place. From the settlement chamber, the liquid is removed by a float-controlled pump and passed through a cross-flow filter and then an activated carbon filter.
U.S. Pat. No. 5,326,469 to Thompson discloses an oil and water separation apparatus wherein a gravity separation is followed by a further removal of oil by reaction with ozone.
Although the prior art methods and apparatus for the separation of oil and water have performed effectively for the separation of free oil, the removal of emulsified oil, for example, with the use of activated carbon has required careful monitoring and frequent replacement of the filter media.
Accordingly, it is an object of this invention to provide an improved method and apparatus for the separation of contaminants from aqueous mixtures and, in particular, the separation of oil from aqueous discharge condensates from compressed air systems.
It is a further object of the invention to provide an oil/water separation system having a more efficient method of filtration for the removal of emulsified oils and other residual contaminants.
It is a still further object to provide a compact and efficient apparatus for the removal of oil from aqueous mixtures.